Many surgical operations involve circulating the blood of a patient through an extracorporeal circuit. In particular, many open-heart surgical procedures require that the patient's heart be stopped, and that various biological functions (i.e., blood circulation and oxygenation) be performed mechanically by various devices included in the extracorporeal circuit. In addition to a pump and to the tubing through which the blood will flow, devices including oxygenators, heat exchangers, and blood accumulation reservoirs may be employed. Each of these devices is monitored and managed by persons who may be present in the operating room, or at remote monitoring and control stations.
One type of blood accumulation reservoir used in such procedures is a venous reservoir. The venous reservoir serves as a receptacle for blood, typically blood that has been removed from the patient through a vein, which is subsequently oxygenated and further processed prior to being recirculated back to the patient. Thus, the venous reservoir typically serves to collect blood as it first enters the extracorporeal circuit. The use of the venous reservoir enables the operator to control the blood flow rate, blood pressure, blood volume and related parameters necessary to maintaining the patient during the surgical procedure.
A second type of blood accumulation reservoir used in such procedures is a cardiotomy reservoir. The cardiotomy reservoir is used to contain blood which has been collected from the operating field. Blood collected in the cardiotomy reservoir can be reinfused into the patient after being filtered to remove any clots or other unwanted contaminants.
Since the space in the operating room available to operators is often limited, devices have been proposed which combine the venous reservoir and the cardiotomy reservoir in a single structure. In such devices, inlets for the venous blood and for the blood from the operating field are separated from one another. Blood entering the device is filtered and then collected in a common chamber.
These devices, however, are known to have certain disadvantages. For example, the surface area of such devices which comes into contact with the blood is relatively large. As a result, the blood becomes susceptible to damage or coagulation. Additionally, even under relatively normal operating conditions, retrograde blood flow may be induced, causing the blood to be reverse filtered. This is particularly problematic if only venous blood is being collected, because the retrograde flow causes the blood to be sequestered within the cardiotomy filter, thereby reducing the volume of blood available for oxygenation and recirculation to the patient.